Prior art methods of patterning (etching or plating) surfaces with micron or sub-micron features include irradiative lithographic methods such as photolithography, electron-beam lithography, and x-ray lithography. With electron-beam lithography, the beam is rastered across the surface of the article to produce the pattern. This is a slow, expensive process. The equipment used in photo and x-ray lithographic methods do not easily pattern large-areas. The typical photolithographic printer for semiconductor applications has a field area on the order of 1 in.sup.2. These small-area fields must subsequently be stitched together to form a continuous pattern over a large-area substrate. The stitching process is costly and time-consuming.
Accordingly, there exists a need for an improved apparatus and method for patterning large area surfaces with sub-micron features, which easily, economically, and reproducibly prints large-area fields, thereby providing high throughput.
Photolithographic aligners are known in the art. They are designed to align hard masks, which are rigid and planar. This is accomplished by aligning one or more alignment patterns on the hard mask with the corresponding one or more alignment patterns on the surface to be patterned. Thus, the pattern on the mask is brought into registration with the pattern on the surface. The alignment is accomplished by making the necessary displacements of the entire hard mask. Since the hard mask is not deformable, it does not tend to bow or otherwise mechanically distort in a manner which can distort the pattern of the mask.
The alignment and contact printing process in photolithographic equipment includes several steps. The mask is placed in a photomask holder. The substrate to be patterned, or wafer, is placed on a vacuum chuck, which includes a perforated plate. When the article is placed on the surface of the vacuum chuck, it is held in place by suction through the holes in the plate. The hard mask is then positioned above, and parallel to, the wafer, within several hundred microns. A prealignment is performed wherein one or more alignment patterns on the hard mask are brought into registration with one or more corresponding alignment patterns on the surface of the substrate or wafer. Depending on the geometry of the corresponding patterns, one or two pairs of alignment patterns are sufficient to bring the stamp printing pattern into registration with the overall wafer pattern. This is true regardless of the size of the mask. The alignment is accomplished by detecting the relative positions of the alignment patterns and making the necessary adjustments in the position of the hard mask and/or wafer by making x-y adjustments and angular/rotational adjustments in position. When alignment is achieved, the hard mask and substrate or wafer are brought into contact. The printing gap between the mask and wafer is 0-50 microns: hard contact is achieved by providing a high vacuum between the mask and wafer; soft contact is achieved by providing a low vacuum, about 50-500 mm Hg.
If the above method is utilized to contact a deformable, flexible stamp with a surface of a substrate, complete adhesion is often not achieved between the surface of the flexible stamp and the surface of the substrate. It is also extremely difficult to apply uniform pressure on the elastomeric stamp across the substrate. A prior art aligner would fail to properly contact a flexible stamp in a stamping process, resulting in non-reproducible and non-uniform printing. To be of any practical use, a stamping technique needs to provide reproducibility and uniformity.
Accordingly, there exists a need for an improved apparatus and method for using a flexible stamp to define micron and sub-micron features on the surface of an article and for stamping the surface so that the pattern on the flexible stamp is transferred reproducibly and uniformly.
Micro-contact printing of self-assembled molecular monolayers (SAMs) is known in the art. The SAMs are comprised of molecules, which have a functional group that chemically binds to certain types of solids. The remainder of the molecule (usually a long-chained hydrocarbon) interacts with neighboring molecules to form a dense structure which acts as a diffusion barrier to chemical species. Current micro-contact printing methods for producing a SAM on a surface, including the stamp aligner proposed in U.S. Pat. No. 5,725,788, issued Mar. 10, 1998, entitled "Apparatus and Method for Patterning a Surface", and copending U.S. patent application Ser. No. 08/978,797, filed Nov. 26, 1997, entitled"Micro-Contact Printing Stamp", and assigned to the same assignee, which apparatus is hereby incorporated by reference, cannot reliably or reproducibly print surfaces with micron and sub-micron features. This is attributed to the way contact is made and broken between the stamp and wafer.
Accordingly, the purpose of the present invention is to provide a cost-effective, reproducible method for patterning large-area surfaces using micro-contact printing of self-assembled molecular monolayers via an improved method to bring the stamp into and out of contact with the wafer.